The Atoms and the Periodic Table: Introduction
Copper is one of the many naturally occurring substances that people use for making electric wires, tools, and building materials. Copper is an example of matter. Look around you; there are many different types of matter in your environment. Matter can be solid, liquid, or gas. Matter is any substance that has mass and occupies space. Mass is a property of matter related to the amount of material an object has.
Matter’s ability to take up space leads us to another question: What makes up matter? To answer this question, consider a shiny piece of copper and perform the following thought experiment: Imagine cutting a piece of copper in half. How would the two pieces compare to the original sheet? Clearly, they would be smaller in size, but would their identity change? Wouldn’t they still be made up of copper? Now imagine cutting these two pieces in half again. Would their identities change as a result of the second cut? The answer is no.
If you were able to cut the copper pieces into half indefinitely, at what point would you attain the smallest possible piece of copper? How small would this piece of copper be? What would it look like? How would it compare to the smallest piece of some other type of matter such as iron or water? These are questions to keep in mind as you explore chemistry, which is the study of changes in matter.
1.1 Atomic Structure
Today we use the atomic theory to explain that a piece of copper is composed of copper atoms and that a copper atom is the smallest piece of copper that can exist. Even though atoms are too small to be seen through most microscopes, scientists have gathered a great deal of experimental evidence to support the atomic theory—the idea that atoms are the basic building blocks of matter.
Atomic Theory
The ancient Greeks developed the idea that matter is composed of small particles that cannot be divided. This idea continued to survive throughout history, but without experimental evidence it was not widely accepted. Finally, in the early 1800s, an Englishman named John Dalton saw a pattern in numerical data and used that pattern as evidence to support the atomic theory.
Dalton’s Atomic Theory and the Elements
Dalton observed that whenever two substances combined to produce a new substance, called a compound, they always combined in the same proportion (by mass). In other words,if one experiment showed 10 grams of substance A combining with 20 grams of substance B in a reaction, then this same 1:2 mass ratio of the reaction would be observed no matter what quantities of substances were used.
Dalton observed this constancy in mass ratio when substances combine on a large scale, and he hypothesized that the same also applies on the smallest possible scale. He proposed that matter is formed of individual particles that have specific masses and react with each other in whole number ratios. These particles were atoms.
Dalton’s atomic theory covered several ideas about atoms. The theory proposed that the simplest substances found in nature are called elements. Each element consists of identical tiny particles called atoms. Dalton described atoms as indivisible particles that formed the basis for all matter. Examples of elements are gold, oxygen, iron, and copper.
Dalton’s theory also proposed that atoms in one piece of matter could differ from atoms in another piece of matter. For example, the atoms in a sheet of copper differ from the atoms in a sheet of iron. These two different types of atoms represent two different elements.
At the time Dalton proposed his atomic theory, 36 elements were known. Some of these elements and the symbols Dalton used to represent them are summarized in Figure 2.
Fill in the blank.
Dalton observed that when any two substances combined to produce a new substance, the two substances always combined in
proportion by mass.
answer :
same
Fill in the blank.
A(n)
answer :
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